Primary visual transduction, as accomplished by the photoreceptor cells of the retina, is accomplished and regulated by a vast array of molecular machinery. Of the many protein components that play some role in visual transduction only the molecular photoreceptor rhodopsin is fairly well characterized. We have initiated a program to isolate and characterize other less abundant components. We have now purified and characterized cGMP phosphodiesterase and a GTP binding protein, and are developing procedures to isolate several other key components such as opsin kinase, quanylcyclase, and phospho-opsin phosphatase. To test the mode of light activation of these enzymatic activities and their functional role in visual transduction, in vitro reconstituted systems of artificial membranes containing the photoreceptor rhodopsin and various combinations of the enzymes are examined. The current techniques of molecular biology now enable investigators to determine the nucleotide sequence coding for proteins hence establishing the primary amino acid sequence, to examine gene expression, and to amplify the amounts of eucaryotic proteins available for study. To take advantage of these techniques we have isolated mRNA for bovine opsin and cloned the cDNA copy of mRNA. Characterization and sequencing of the cloned DNA are underway. These probes will allow us to initiate molecular studies of photoreception at the genetic level.